Money. The US is abolutely non-competitive, the French have a site in South America close to the equator but has limited use because of costs, and Sea Launch (US west coast assembly site) went bankrupt and just got back into business. Meanwhile , the Russians set up an assembly line and went for low prices to get market share. Their problem is their launch site in the far north and the satellite has to use up a significant amount of it's fuel to move the orbit inclination from 51 degrees to 0 degress. If things were to start over, the French or Sea Launch would have a good change of getting the volume they need to be competitive but now they have to chip away at the Russian market share.
I think the launch with a 51 degree inclination impacts the Proton's mass to geostationary transfer orbit capabilities, however, the satellite does not have to use up it's fuel any more than an Cape Canaveral or even Sea Launch bird. The Breeze-M is makes one final burn to go from 51 degrees to 18 degrees, leading to a standard required delta-V (I believe I've seen literature stating 1800 m/s, same as any any launcher, I believe) to get to Geostationary.
For instance one thing you notice about ILS target is a bit further than Sea Launch target perigee. Echostar 11, for example, went into orbit from Sea Launch with zero degree inclination, but a 35643x750 km orbit, while Quetzsat-1 had a target of 18.6 inclination, but 35786x5983 orbit. An orbit that needs flattened, but needs less fuel to get to circular.
There is one US launcher using the Delta II, Delta IV and Atlas V, but they are kept busy with government launches, and as was mentioned, is pricier than the Russians. But they have done some commercial work. For instance in 2009 they launched Intelsat 14 and the ICO G1 sat in 2008, both of which were just too big for the Proton.
Arianespace, the French launcher, becomes quite cost competitive when you lose it's superior mass to GTO capabilities to launch two small or medium sats. Dish sats of late, though, are too beefy to share a launch, thus ILS is the cheapest option for them.
